This application generally relates to data communications and, more particularly, to data processing for transmission in a multi-channel communication system.
A multi-channel communication system may refer to a wireless communication system capable of transmitting information such as voice and data between a transmitter and a receiver, which may have more than one transmitter antenna and receiver antenna, respectively. Such a multi-channel system may include, for example, a multiple-input multiple-output (MIMO) communication system, an orthogonal frequency division modulation (OFDM) system and a MIMO system based on OFDM. A MIMO system may employ multiple transmitter antennas and multiple receiver antennas to exploit spatial diversity to support a number of spatial subchannels, each of which may be used to transmit data. An OFDM system may partition an operating frequency band into a number of frequency subchannels, each of which is associated with a respective subcarrier on which data may be modulated. A multi-channel communication system thus may support a number of “transmission” channels,” each of which may correspond to a spatial subchannel in a MIMO system, a frequency subchannel in an OFDM system, or a spatial subchannel of a frequency subchannel in a MIMO system that utilizes OFDM.
In a multi-channel communication system, however, transmission channels may experience different channel conditions due to, for example, different fading and multipath effects, and may therefore result in different signal-to-interference-plus-noise ratios (SNRs). Consequently, the transmission capacities (i.e., the information bit rates) that may be supported by the transmission channels for a particular level of performance may be different from channel to channel. Moreover, the channel conditions may often vary over time. As a result, the bit rates supported by the transmission channels may also vary with time. To alleviate the channel effects, a coding and modulation scheme (MCS) may be configured to process data prior to transmission via the channels so as to enhance transmission capacities. The MCS may be divided into a single codeword (SCW) architecture and a multi codeword (MCW) architecture.
FIG. 1A is a schematic block diagram of a prior art transmitter 1 based on an SCW scheme in a MIMO system. Referring to FIG. 1A, the transmitter 1 may include an encoder 11, a rate matcher 12, a channel interleaver 13, a modulator 14, a layer mapper 15, a precoder 16, a number of antennas 17-1 to 17-n and a controller 18. The encoder 11 receives a code block containing information bits in a bit stream. Encoder 11 then encodes the received information bits with a code scheme, for example, a 1/3-rate Turbo code (TC) with tail bit addition. In the rate matcher 12, rate matching is performed under the control of the controller 18, which in turn may receive a feedback signal from a receiver to determine a code rate for the channel.
FIG. 1B is a flow diagram illustrating prior art data processing in terms of bit size in the transmitter 1 illustrated in FIG. 1A. Referring to FIG. 1B and also FIG. 1A, at step 110, a number of “Nb” information bits are received by the encoder 11. At step 120, after the 1/3-rate Turbo coding and the addition of, for example, twelve (12) tail bits, the coded bits have a size of (3 Nb+12) bits. At step 130, puncturing or repetition, depending on the channel condition, may be performed in the rate matcher 12, resulting in an output of Np bits, where Np is the total amount of bits to be transmitted. The number of Np, and in turn the code rate Nb/Np, may be determined by the controller 18 according to the channel condition. At step 140, the Np bits are interleaved in the channel interleaver 13. At step 150, the modulator 14 modulates the interleaved Np bits and generates a number of “Np/m” symbols, where the value “m” may also be determined by the controller 18. Next, at step 160, the modulated Np/m symbols are de-multiplexed in the layer mapper 15 before precoded in the precoder 16. For simplicity, it may be assumed that two antennas 17-1 and 17-2 are utilized to transmit Np/2 m symbols each.
Although the SCW scheme described and illustrated with reference to FIG. 1A may have a relatively simple structure and a relatively low feedback overhead, the performance such as error probability and data rate may not be desirable. Furthermore, due to the time-varying nature of link conditions, the channel 17-1, for example, may have a better link condition than the channel 17-2 during a certain period of transmission and therefore should transmit more coded bits or more important bits than the channel 17-2. However, in the transmitter 1, the channels 17-1 and 17-2 transmit substantially the same number of coded bits, which may not enhance the transmission capacities. Moreover, important bits and less important bits are not separated from each other and may be evenly transmitted in the channels 17-1 and 17-2.
FIG. 2A is a schematic block diagram of an exemplary transmitter 2 based on an MCW scheme in a MIMO system. Referring to FIG. 2A, the transmitter 2 may include a splitter 29, encoders 21-1 to 21-n, rate matchers 22-1 to 22-n, channel interleavers 23-1 to 23-n, modulators 24-1 to 24-n, a layer mapper 25, a precoder 26, antennas 27-1 to 27-p and a controller 28. The splitter 29 may divide incoming information bits into a number of “n” groups. Each group of information bits is then processed in an independent path, for example, a path 20 in a dashed block including the encoder 21-1, rate matcher 22-1, channel interleaver 23-1 and modulator 24-1. A modulated symbol from the path 20 may subsequently be processed by the layer mapper 25 and the precoder 26 before transmitted on one or more of the antennas 27-1 to 27-p. In the transmitter 2, the controller 28 can determine a code rate for each channel according to a feedback signal from a receiver. The feedback signal may include information on a link condition of each channel measured at the receiver.
FIG. 2B is a flow diagram illustrating data processing in terms of bit size in the transmitter 2 illustrated in FIG. 2A. Referring to FIG. 2B and also FIG. 2A, at step 210, the splitter 29 receives a number of Nb information bits. Then, at step 220, the splitter 29 splits the Nb bits into “n” groups of bits. For simplicity, two groups of bits, i.e., n=2, are illustrated. Accordingly, the Nb bits may be divided into a first group containing Nb,0 bits and a second group containing Nb,1 bits, where Nb=Nb,0+Nb,1. At step 230, the 1/3-rate TC with tail bit addition coding scheme is performed in the encoders 21-1 and 21-2, which then respectively generate Nc,0 bits and Nc,1 bits, where Nc,0 and Nc,1 satisfy Nc,0+Nc,1=3 Nb+12. At step 240, rate matching including puncturing or repetition is performed in the rate matchers 22-1 and 22-2, each of which generates an output of Np/2 bits, where Np is the total amount of bits to be transmitted. At step 250, two groups of Np/2 bits are interleaved in the channel interleavers 23-1 and 23-2, respectively. At step 260, each of the modulators 24-1 and 24-2 modulates the Np/2 bits and generates a number of Np/2 m symbols. At step 270, the modulated Np/2 m symbols are de-multiplexed in the layer mapper 25 before precoded in the precoder 26. For simplicity, it may be assumed that two antennas 27-1 and 27-2 are utilized to transmit the Np/2 m symbols each.
The transmitter 2 shown in FIG. 2A can enhance transmission capacities. For example, assuming that the channel 27-1 is better than the channel 27-2 in a certain time duration, the controller 28 may increase the puncturing rate in the rate matcher 22-1 so that the channel 27-1 may support more information bits. Nonetheless, the transmitter 2 may require a relatively complicated hardware structure. Furthermore, a total number of “n” decoders may be required at the receiver side, which may dramatically increase the cost of the MIMO system.